The invention relates to a hull for a sail boat with a stern.
All watercraft have the special feature that the optimum, most favorable hull shape shows its optimum properties only at a precisely predetermined speed. However, all yachtsmen attempt to convert any wind force into the highest possible travelling speed, which is not possible with existing stern shapes.
The majority of water craft are subdivided by their hull shape into three groups, namely:
watercraft with a displacement-type hull; particularly suitable for heavy craft and moderate speeds
watercraft with a semi-planing-type hull; and
watercraft with a planing-type hull, particularly suitable for fast and not too heavy craft.
The advantage of a displacement-type hull is low water resistance at low speed and excellent seaworthiness in heavy seas, particularly in the case of aft waves. However, a serious disadvantage of this stern shape is that at the so-called hull speed the water resistance increases very considerably. The suction resulting from the stern wave holds the boat firm and, e.g., when the boat is being towed by powerful tugs, this can mean that the boat is pulled below the surface of the water.
The prior art semi-planing-type hull is more favorable from this standpoint, since is breaks off a heavy stern wave by the breakdown stern over the waterline. However, it suffers from considerable disadvantages in rough seas and more particularly with aft waves, since fairly large waves pass over the boat.
The planing hull type can be used only on heavily motorized and very light boats, since at low speeds the broken-off stern dips into the water, thereby causing a very high resistance.